/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.servlet.resource;

import java.util.List;

import javax.servlet.http.HttpServletRequest;

import org.springframework.cache.Cache;
import org.springframework.cache.CacheManager;
import org.springframework.core.io.Resource;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;

/**
 * A {@link org.springframework.web.servlet.resource.ResourceResolver} that
 * resolves resources from a {@link org.springframework.cache.Cache} or otherwise
 * delegates to the resolver chain and saves the result in the cache.
 *
 * @author Rossen Stoyanchev
 * @author Brian Clozel
 * @since 4.1
 */
public class CachingResourceResolver extends AbstractResourceResolver {

    public static final String RESOLVED_RESOURCE_CACHE_KEY_PREFIX = "resolvedResource:";

    public static final String RESOLVED_URL_PATH_CACHE_KEY_PREFIX = "resolvedUrlPath:";


    private final Cache cache;


    public CachingResourceResolver(Cache cache) {
        Assert.notNull(cache, "Cache is required");
        this.cache = cache;
    }

    public CachingResourceResolver(CacheManager cacheManager, String cacheName) {
        Cache cache = cacheManager.getCache(cacheName);
        if (cache == null) {
            throw new IllegalArgumentException("Cache '" + cacheName + "' not found");
        }
        this.cache = cache;
    }


    /**
     * Return the configured {@code Cache}.
     */
    public Cache getCache() {
        return this.cache;
    }


    @Override
    protected Resource resolveResourceInternal(@Nullable HttpServletRequest request, String requestPath,
            List<? extends Resource> locations, ResourceResolverChain chain) {

        String key = computeKey(request, requestPath);
        Resource resource = this.cache.get(key, Resource.class);

        if (resource != null) {
            if (logger.isTraceEnabled()) {
                logger.trace("Found match: " + resource);
            }
            return resource;
        }

        resource = chain.resolveResource(request, requestPath, locations);
        if (resource != null) {
            if (logger.isTraceEnabled()) {
                logger.trace("Putting resolved resource in cache: " + resource);
            }
            this.cache.put(key, resource);
        }

        return resource;
    }

    protected String computeKey(@Nullable HttpServletRequest request, String requestPath) {
        StringBuilder key = new StringBuilder(RESOLVED_RESOURCE_CACHE_KEY_PREFIX);
        key.append(requestPath);
        if (request != null) {
            String encoding = request.getHeader("Accept-Encoding");
            if (encoding != null && encoding.contains("gzip")) {
                key.append("+encoding=gzip");
            }
        }
        return key.toString();
    }

    @Override
    protected String resolveUrlPathInternal(String resourceUrlPath,
            List<? extends Resource> locations, ResourceResolverChain chain) {

        String key = RESOLVED_URL_PATH_CACHE_KEY_PREFIX + resourceUrlPath;
        String resolvedUrlPath = this.cache.get(key, String.class);

        if (resolvedUrlPath != null) {
            if (logger.isTraceEnabled()) {
                logger.trace("Found match: \"" + resolvedUrlPath + "\"");
            }
            return resolvedUrlPath;
        }

        resolvedUrlPath = chain.resolveUrlPath(resourceUrlPath, locations);
        if (resolvedUrlPath != null) {
            if (logger.isTraceEnabled()) {
                logger.trace("Putting resolved resource URL path in cache: \"" + resolvedUrlPath + "\"");
            }
            this.cache.put(key, resolvedUrlPath);
        }

        return resolvedUrlPath;
    }

}
